In hand held optical character readers such as that described in U.S. Pat. No. 4,075,605 it is possible for the operator to read a character two or more times. This is caused by poor scanning motion by the operator. When the scanning motion is such that a character is being read at either the top or bottom of the scanning array the character can move out of and then back into the array since the white path block conditioning is ignored unless there is white above and below the character. Character presence is lost as soon as the first or last row of the array is found to contain black data. When the character moves back into the scanning array a new character presence is detected and the character is read again.
When a character is read more than once there are two possible indications to the operator. If all the other characters are read then the field will be too long and will not pass the edit rules. This is in a system where fixed fields are read a certain number of characters are in each field. For example, if the line D1234 is scanned such that 2 goes out the top of the array and then comes back, the resolved decision string would be 12234. Since the edit function was checking for a four digit D field the five digit field would be rejected. This is recorded as a "no read". If the same motion that was used to cause the long field was to be repeated but starting past the 4, the resolved decision string would be D1223. This four digit D field would pass the edit rules. However, it would be an incorrect reading of the field which may or may not be noticed by the operator. Even though there apparently was a good reading, the data base would contain two substitutions, an extra 2 and no 4.